Conventional protective electrical devices, such as surge arresters, provide protection for equipment of power distribution systems during fault conditions caused by a system disturbance, such as a lighting strike. An overload of current resulting from a system disturbance can damage and/or destroy electrical equipment because the amount of current is much greater during the disturbance relative to during normal operating conditions.
Conventional surge arresters include an outer housing with two end terminals for connecting the arrester between a conductor device, such as a bushing insert, and ground. Held within the housing of a conventional arrester is a stack of arrester elements or metal oxide varistor (MOV) blocks. The MOV blocks allow the arrester to divert the overload current through the arrester to ground, thereby protecting the electrical equipment. In particular, as the voltage applied to the MOV blocks is increased, due to a system disturbance, the impedance of the MOV blocks decreases towards zero and the blocks become highly conductive thereby conducting the resulting current overload to ground.
Typically during fault conditions, conventional surge arresters rupture and separate from the bushing insert of the electrical equipment, to which it was connected. Arcing typically occurs within the arrester resulting in the generation of gas and heat as the internal arrester elements vaporize. During such a catastrophic failure, the arrester will rupture due to the generated gases that cannot be vented quickly enough from the arrester housing. Commonly, the housing ruptures in random areas, particularly near the connection of the bushing insert and the arrester, thereby forcing the arrester away from the bushing insert such that the arrester separates from the bushing insert. The conventional arresters fail to provide a mechanism for preventing separation of the arrester from the bushing insert during a fault event.
Examples of conventional arresters are disclosed in U.S. Pat. Nos. 6,014,306 to Berlovan et al.; 6,008,975 to Kester et al.; 5,633,620 to Doerrwaechter; 5,309,313 to Yaworski et al.; 5,088,001 to Yaworski et al.; 5,043,838 to Sakich; and 4,463,405 to Koch et al.
Accordingly, an object of the present invention is to provide an electrical device for a power distribution system and a method of making same that provides protection for the system equipment during a fault condition.
Another object of the present invention is to provide an electrical device for a power distribution system and a method of making same that provides a mechanism for limiting separation of the electrical device from an electrical connector of the system.
Yet another object of the present invention is to provide an electrical device for a power distribution system and a method of making same that provides a weak section in the housing of the device that allows controlled venting of internal gases upon rupture of the housing.
The foregoing objects are basically attained by an electrical device, comprising a housing including first and second portions with each of the first and second portions having a first insulative layer and a second conductive layer. The first layer defines an inner cavity, and the second portion has opposing first and second lateral sides. The first layer defines a first thickness at the first lateral side and a second thickness at the second lateral side. An electrically conductive member is received within the inner cavity in the first portion. At least one electrical component is received within the inner cavity at the second portion. A weak section in the first lateral side of the second portion of the housing is defined by the first thickness at the first lateral side that is substantially less than the second thickness at the second lateral side diametrically opposite thereto at given points along a longitudinal axis of the second portion.
The foregoing objects are also basically attained by a method of making an electrical device, comprising the steps of forming an outer conductive layer, forming the inner cavity in first and second portions thereof and placing a mandrel in the inner cavity of the second portion of the conductive layer. The mandrel has a teardrop cross sectional shape. Molding an inner insulative layer by injecting a substantially resilient insulative material into the inner cavity at a second portion of the housing and around the mandrel, thereby forming an inner cavity in the insulative layer into teardrop cross-sectional shape that is substantially identical to the tear drop cross-sectional shape of the mandrel.
By fashioning the electrical device in this manner, a controlled venting of internal gases is provided through the weak section. Arranging the weak section rupture in a direction away from an electrical connector device to which the electrical device is connected to avoid disconnection.